DARPA conducted the flights in collaboration with Northrop Grumman and the NASA Dryden Flight Research Center using two NASA Global Hawk UASs.

The agency said that the two Global Hawks successfully flew in close formation (as close as 30 feet) for more than 2.5 hours at 44,800 feet. The close formation flight showed the ability of UAS to operate autonomously under in-flight refueling conditions.

"The technical developments that enabled these two high-altitude, long-endurance unmanned Global Hawks in close formation is an outstanding accomplishment for the AHR program," said Fred Ricker, vice president and deputy general manager for Northrop Grumman Aerospace Systems' Advanced Programs & Technology. "Coupled with the advanced design and technical implementation of aerial refueling systems on board both aircraft, the demonstration has truly brought a concept to life, which has the potential to change the operations for unmanned aircraft utility and enable mission flexibility never before realized."

(Northrop Grumman, DARPA and NASA Dryden Flight Research Center successfully completed a series of flight demonstrations, moving the DARPA's Autonomous High-Altitude Refueling program closer to demonstrating the first autonomous aerial refueling between two unmanned, high-altitude aircraft. The flights, which used two NASA Global Hawk unmanned aircraft -- one configured as a tanker and the other as a receiver -- were conducted at Edwards Air Force Base, Calif.)